The embodiments disclosed herein relate to electronic devices and more particularly to the dissipation of heat generated by microprocessors.
In operation, microprocessors and other electronic devices generate heat. Excess heat can damage the device if it is not dissipated. Therefore, generally microprocessors and other heat-generating electronic devices utilize heat dissipating structures or heat sinks as a conductor to dissipate excess heat. A conventional configuration for dissipating heat from a microprocessor is to mount a heat sink of a metal material (such as aluminum or copper) over the microprocessor. Mounting a metal heat sink directly over the microprocessor is not a favored practice, because of the poor conductivity achieved by the union of the metal heat sink and the microprocessor. In addition, the surface of the heat sink material is generally comprised of micro-pores or surface roughness and the surface of the microprocessor has a crown shape. Accordingly, the union of a heat sink and the microprocessor is not uniform leading to the presence of air pockets and poor thermal conductivity. Therefore, a thermal interface material, such as thermal grease, a thermal elastomer, or a phase-change material is interposed between the microprocessor and the heat sink. The thermal interface material provides improved thermal conductivity between the processor and the heat sink. The thermal interface material tends to fill the micro-pores and therefore makes the transition between the microprocessor and the heat sink more uniform.
A microprocessor or other heat-generating electronic device generally is affixed to a printed circuit board (PCB). In the case of a microprocessor, a heat sink is usually affixed to the PCB through bolts or screws with an established gap or bond line thickness between the heat sink and the microprocessor. In portable computer applications, for example, the bond line thickness associated with conventional microprocessor packaging is approximately 5 milsxc2x12 mils, the difference generally attributable to differences in microprocessor heights. It is desirable, in one sense, to establish a consistent bond line thickness. One way this is established is by securing the heat sink to the PCB under pressure. The amount of pressure that may be applied to heat sink affixation is limited, however, to about 20 to 100 pounds per square inch to avoid damage to the microprocessor. The amount of compression that a thermal interface material can withstand is also limited. Thermal interface material under compression tends to flow out of the gap between the heat sink and the microprocessor under compression and additionally tends to dry out with power cycling. The compressive limitation of the thermal interface material reduces the reliability of the thermal interface material.
Despite its limitations, it is desirable to use thermal interface material between a heat sink and a microprocessor or other heat-generating electronic device. What is needed is a configuration whereby thermal interface material may be utilized and the reliability issues present in prior art configurations can be avoided.